Tory majorities were slashed in the latest council by-elections which saw Labour go ahead over the month.
Analysis of 16 comparable results in September suggests a projected 3.4% margin for the party over Conservatives.
A calculation based on 10 wards fought both times by all three major parties gives a line-up of: Lab 34.9%, C 32.7%, Lib Dem 17.3%.
These figures do not include two results from King's Lynn in Norfolk which will be declared later today.
A late surge to Labour secured its September lead, overcoming a poor performance last week.
However there was some cheer for Tories when they comfortably defended a Hampstead Town seat in north London's Camden Borough.
The ward is covered by Hampstead and Kilburn, Labour's most marginal parliamentary constituency where ex-minister and actress Glenda Jackson had a majority of 42 votes in the 2010 General Election when council polls were on the same day.
This week's by-election showed a swing of just 1.3% from Tory to Labour since then.
This is in line with London's mayoral and assembly elections in May and later borough by-elections in the capital showing Conservative support holding up better than in the rest of the country.
The one crumb of comfort for Liberal Democrats in their conference week is that they kept their second place at Hampstead Town after a miserable performance in May.
Blaby District - Pastures: C 442, Lab 281. (May 2011 - Two seats C 1,103, 905, Lab 483, 349). C hold. Swing 9.6% C to Lab.
Camden London Borough - Hampstead Town: C 1,040, Lib Dem 695, Lab 512, Green 207. (May 2010 - Three seats C 2,261, Lib Dem 2,198, C 2,159, 2,006, Lib Dem 1,775, 1,681, Lab 1,113, 757, 728, Green 528, 349, 303). C hold. Swing 1.3% C to Lab.
Dartford Borough - Castle: C 191, Lab 111, Ukip 60, Swanscombe and Greenhithe Residents Association 50, English Democrats 32. (May 2011 - C 337, Lab 122, Swanscombe and Greenhithe Residents Association 83, English Democrats 56). C hold. Swing 8.9% C to Lab.
King's Lynn and West Norfolk Borough - Spellowfields: Counting today. (May 2011 - Two seats C 524, 456, Ind 450, 429, Lab 347).
Middlesbrough Borough - North Ormesby and Brambles Farm: Lab 471, Lib Dem 109, Ind 71, C 38, No description 6. (May 2011 - Two seats Lab 803, 606, C 169). Lab hold. Swing 0.4% C to Lab.
Norfolk County - Clenchwarton and King's Lynn South: Counting today. (June 2010 - C 1,015, Lib Dem 743, BNP 313, Lab 301, Green 214).
Runnymede Borough - Chertsey Meads: C 450, Lab 312, Ukip 312, Lib Dem 34, Monster Raving Loony Party 10. (May 2012 - C 624, Ukip 281, Lab 239, Lib Dem 96). C hold. Swing 9.3% C to Lab.
Runneymede Borough - New Haw: C 346, Lab 148, Ukip 124, Lib Dem 54. (May 2012 - C 577, Lab 218, Ukip 176, Lib Dem 120). C hold. Swing 1.7% C to Lab.